Pressure transformer

ABSTRACT

A pressure transformer including a plurality of pistons. Each of the pistons is driven through a working stroke and a return stroke by fluid under pressure and acts as a fluid motor. Each of the pistons is supplied with fluid, and on the working stroke, the piston increases or decreases the pressure of the fluid supplied thereto. Each of the pistons also serves as a valve to control the movement of one of the other pistons.

Willie 11 Henry States atent 1191 PRESSURE TRANSFORMER [75] inventor:Augustus P. liienry, lrvine, Calif. [731 Assigneei Bates Gerla etenzlryissrQs iLs [22] Filed: Apr. 6, 1973 [21] Appl. No.: 348,861

[52] US. Cl 417/225, 417/349, 417/401,

'9l/4 77' [51] lint. Cl. F041) 17/00 [58] Field of Search 417/225, 226,227, 392, 417/401, 339, 349; 91/477, 192

[56] References Cited UNITED STATES PATENTS 3,675,539 7/1972 Zajac etal.... 91/477 2,579,670 12/1951 Hjarpe 417 225 [111' 9,899,592 1451 May7,1974

8/1942 Ponting ..417/22'5 3/1959 00111011 et a1. ..417/271 PrimaryExaminer-William 1. Freeh Assistant ExaminerGregory Paul LaPointeAttorney, Agent, or Firm-Smyth, Roston & Pavitt [57] ABSTRACT A pressuretransformer including a plurality of pistons. Each of the pistons isdriven through a working stroke and a return stroke by fluid underpressure and acts as a fluid motor. Each of the pistons is supplied withfluid, and on the working stroke, the piston increases or decreases thepressure of the fluid supplied thereto. Each of the pistons also servesas a valve to control the movement of one of the other pistons.

'16 Claims, 5 Drawing Figures PATENTEMAY 7 I974 3.809.502

sum 1 [1F 3 PATENTEDMY 71914 3.809 502 SHEU 3 0F 3 BACKGROUND or THEINVENTION A pressure intensifier may include at least two reciprocablepistons driven by fluid at supply pressure to elevate the pressure ofsome of the supply fluid to a discharge pressure. To reciprocate thepistons, appropriate valving is provided to control to control the flowof fluid to and from the pistons. The valving is separate from thepistons, but may be mechanically actuated by the pistons as shown forexample in [1.3. Pat. No. 2,293,076.

SUMMARY OF THE INVENTION One improvement provided by the presentinvention is the incorporation of the valving intothe piston. With thisconstruction, each of the pistons of a pressure intensifier serves as afluid motor, a pump for increasing fluid pressure, and valve means forcontrolling fluid flow to and from the piston and hence for controllingpiston movement. Incorporating the valve into the piston eliminates theseparate valve structure and the control connection therebetween whileretaining the valving function. In addition, the size and weight of thetotal unit is reduced.

The valve is carried by-the piston and is responsive to the position ofthe associated piston to port fluid to at least one other piston. Forexample, the valve may take the form of at least one groove and at leastone land on the piston, in which event, the piston takes on thecharacteristics of a valve spool. The valve may be integral with thepiston. I

If the pistons are to be powered entirely by fluid pressure and solelyby valves integral with the pistons, then the pressure transformer. Eachof the the end of each of its strokes.

To facilitate reciprocating'of the pistons, each of the pistonspreferably has pressure responsive surface means which includes firstand second pressure responsive faces. The valves of a first piston portsfluid at supply pressure to the first pressure responsive face of asecond piston and opens the second face of the second pistons dwells atpiston to a return port to move the second piston on its return stroke.To move the second piston on it working stroke, the second pressureresponsive face is connected to fluid at supply pressure and the firstfluid responsive face is open to the output or discharge of the pressureintensifier. The second fluid responsive face has a larger effectivearea than the first face so that fluid at supply pressure can move thepiston on its working stroke to increase the pressure of the fluidacting against the first pressure responsive face. With thisarrangement, substantially the same fluid which urged the piston on itsreturn stroke is subsequently increased in pressure by the workingstroke of the same piston.

.Another advantage of this invention is that each of the pistons may beidentical thereby reducing manufacturing cost.-

The concepts set forth above have been described with reference to apressure intensifier. However, these concepts are equally applicable toa' pressure reducer.

The invention can best be understood by reference to the followingdescription taken in connection with the accompanying illustrativedrawing.

BRIEF DESCRIPTION OF THE DRAWINGS 7 position.

at least three pistons should be used because two pistons, under thesecircumstances, may not operate satisfactorily. With the concepts of thisinvention to provide a constant flow output, the number of pistonsemployed should be at least three and an odd number or a number whichisan even multiple of an odd number greater than one. For example, fourpistons will operate satisfactorily except the output will notbe aconstant flow.

With the present invention, the pistons are automatically reciprocatedin a predetermined sequence. For example, movement of the first pistonon the working stroke causes the valve means carried thereby to portfluid to the second piston to cause the second piston to move on itsreturn stroke. Movement of the second piston on its return stroke causesthe valve means carried thereby to port fluid to the third piston tomove the third piston on its working stroke. Movement of the thirdpiston on its working stroke causes the valve means carried thereby toport fluid to the first piston to cause the first piston to move on itsreturn stroke. This sequence is continuously repeated during operationof FIGS. 2 and 3 are views similar to FIG. 1 with the pistons being inother operative positions.

FIG. 4 is diagram illustrating relative piston position v ducerconstructed in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a pressuretransformer in the form of a pressure intensifier'll which includes abody 13 and three identical pistons 15, 15a and 15b. Although the body13 is shown as an integral unit housing all three of the pistons 15, 15aand 15b, obviously separate housing units could be used for one or moreof the pistons, if desired.

The body 13 has an inlet port 17 which is adapted for connection tohydraulic fluid, such as oil, at supply pressure. By way of example, theinlet 17 is illustrated in FIG. 1 as being coupled to a pump 19 capableof providing fluid under pressure, such as 3,000 psi, to the intensifier11. Of course, other sources of fluid under pressure may be employed.The body 13 has discharge charged through the return port 23, then thesump 25 can be eliminated. t

The body 13 definesa chamber 27 in which the piston 15 is mounted for.reciprocation. The body 13 has annular grooves 29, 31, 33, 35 and 37 allof which open into the chamber 27..The piston 15 cooperates with thechamber 27 to define chamber sections 39 and 41 at sponding portions aredesignated by corresponding reference numerals followed by the letters aand b, respectively.

The piston 15 has pressure responsive end faces 47 and 49 with the endface 47 having a larger effective area than the end face 49. The piston15 also includes outer lands 51 and 53 and an intermediate land 55. The

lands 51 and 55 are axially spaced to define an annular and continuouslyoperated to provide a continuous outto define a groove 59..

The pistons 15a and 15b are identical to the piston 15 and correspondingportions are designated by corresponding reference numerals followed bythe letters a and b,- respectively.

Passage means provide communication from the ports 17, 21 and 23 to thepistons 15, 15a and 15b. Specifically, a passage 61 providescommunication between the chamber section 39 and the annular groove 35b.Similarly, passages 61a and 61b extend between the chamber section 39aand the groove 35 and from the chamber section 39b to the groove 35a,respectively.

A passage 63 provides communication between the chamber section 41 andthe groove 31b. Similarly, passages 63a and 63b provide communicationbetween the chamber section 41a and the groove 31 and the chambersection 41b and the groove 31a.

The pistons 15 and 15a are also connected by a discharge passage 21a, aninlet passage 17a, and a return or exhaust passage 23a. Similarly, thepistons 15a and 15b are interconnected by a discharge passage 2112, aninlet passage 17b and a return passage 23b. The body 13 also providespassages 45a and 45b which correspond to the passage 45 discussed above.

The various passages extending between the pistons '15, 15a and 15b maybe separate tubes,-or appropriate .grooves, slots, bores, ,etc. in aone-piece body, or may 'be formed in'any other manner known in the art.

I The piston 15 is mounted for reciprocation in the chamber 27. Whenthepiston 15 is moving to the right as viewed in FIG. 1, it is on itsworking stroke. During the working stroke, the pressure responsive endface 49 compresses fluid in the chamber section 41 to thedesireddischarge pressure. When the piston 15 is moving on its return strokecauses the piston 15b to move on its working stroke. Movement of thepistonlSb past null on its working stroke causes the piston 15 to moveput.

More specifically, with the pistons 15, 15a and 15b in the positionshown in FIG. 1, fluid at supply pressure from the inlet port 17 passesthrough the groove 33, the passage 17a, the groove 33a, the passage 17b,the groove 33b, and the groove 59b. As the groove 35b is uncovered bythe piston 15b, the fluid at supply pressure also flows through thepassage 61 to the chamber section 39 to act on the pressure responsiveface 47 of the piston 15. As explained more fully hereinbelow withreference to FIG. 3, ther'e is pressurized fluid in the chamber section41 acting on the pressure responsive face 49. However, because theeffective area of the end face 47 exceeds the effective area of the endface 49, the fluid at supply pressure acting on the face 47 urges thepiston 15 to the right on its workingstroke. Thus, the pressureintensifier 11 utilizes fluid at supply pressure fromthe inlet port 17to drive the piston 15 thereby providing a fluid motor.

A second function of the piston 15 is that as it moves to the right onits working stroke, the fluid in the chamber section 41 is pressurizedto discharge pressure. This fluid at discharge pressure is transmittedfrom the chamber section 41, through the passage 63, the grooves 31b and29b, the passage 21b, the groove 29a, the passage 21a, and the groove 29to the discharge port 21. Thus, a second important function of thepiston 15 is to provide a pumping action which increases the pressure ofthe fluid to provide a high pressure fluid output at the discharge port21.

A third important function of the piston 15 is to provide integral valvemeans for various purposes including moving the piston 15a on its returnstroke. In the position shown in FIG. 1, the piston 15 is at a null orcentered position, and the piston 15a is at an extreme right-handposition and is about to begin its return stroke. The piston 15b is atan-extreme lefthand position and is the next piston to move on a workingstroke. In the null position of the valve 15, it closes off the chambersections 39a and 41a from the ports 17, 21 and 23. When the piston 15amoves slightly to the right of the position shown in FIG. 1, the land 55uncovers the groove 33 to provide communication between the inlet port17 and the groove 57. This causes fluid at supply pressure to flowthrough the groove 57, the groove 31 and the passage'63a to the. chambersection 41a where it acts on th pressure responsive end face 49a of thepiston 15a. Simultaneously, the land 53 uncovers the groove 37 to openthe groove 59 to the return port 23. This in turn provides communicationbetween the chamber section 39a and the return port 23 through thepassage 6 1a and the groove 35. As the piston 15 moves to the right ofthe null position, the land 51 continues to block the chamber section41a from communication with the discharge port 21a. Thus, fluid atsupply pressure acts on the end face 49a, and the end face 47a is opento the return port 23. Accordingly, the piston 15a is moved to the lefton its return stroke by this differential fluid pressure notwithstandingthe smaller effective area of the end face 49a.

Movement of the piston 15a to the left on its return stroke provides thenecessary valving action to cause movement of the piston 15b to theright on its working stroke. In the position shown in FIG.'2, the piston15 is at the end of its working stroke, the piston 15a is at the end ofits return stroke, and the piston b is at a null or centered positionduring its working stroke. As shown in FIG. 2, movement of the piston15a on its return stroke provides fluid at supply pressure to thechamber section 3% and opens the chamber section 41b to the return port23. Specifically, the groove 59a of the piston 15a providescommunication between the passage 61b leading from the chamber section39b and the inlet passage 17a whereby fluid at supply pressure isprovidedto the chamber section 39b to act on the end face 47b.Similarly, the groove 57a provides communication between the passage 63bleading from-the chamber section 41b and the discharge passage 21a sothat the chambersection 41b is connected to the discharge port 21. Withthis valving operation, the piston 15b is moved to the right on itsworking stroke in the same manner described hereinabove with referenceto the working stroke of the piston 15. Thus, the piston 15b operates asa fluid motor and a pump to deliver hydraulic fluid at dischargepressure to the discharge port 21.

FIG. 3 shows the pressure intensifier 11 with the piston 15 at the endof its return stroke, the piston 150 at a null position during itsworking stroke, and the piston 15b at the end of its working stroke. Thepiston 15b similarly operate the pistons 15b and 15, respectively.

FIG. 4 is a diagram showing the sequence of operation of the pistons15a, 15b and 150. The ordinate repcarries valve means which operate tomove the piston 15 on its return stroke during the working stroke of thepiston 15b. Specifically, as the piston 15b moves to the right of thenull position shown in FIG. 2, the groove 59b provides communicationbetween the return passage 23b and the passage 61 leading to the chambersection 39. Thus, the pressure responsive face 47 is open to the returnport 23. Simultaneously, the groove 57b provides communication betweenthe inlet passage 17b and the passage 63 leading to the chamber section41. Thus, fluid at supply pressure acts on the pressure responsive face49. This moves the piston 15 on its return stroke. I

As the piston 15 moves on its return stroke, it provides valving actionto move the piston 15a on its working stroke. Specifically, the groove59 allows fluid at supply pressure to flow from the inlet port 17through the passage 61a to the chamber section 39a. Simultaneously, thegroove 57 provides communication between the passage 63a which leadsfrom the chamber section 41a to the discharge port 21.

From the foregoing, it should be apparent that each piston, as it moveson its working stroke, provides the necessary valving action to causeone of the other pistons to move on its return stroke. In addition, aseach piston moves on its working stroke, it provides the necessaryvalving action to close off the piston which has just completed itsworking stroke from the discharge port 21. Each of the pistons as itmoves on its return stroke provides the necessary valving action tocause one of the other pistons to move on its working stroke.

In summary, the valve means carried by the piston 15 selectivelyprovides communication between the ports 17, 21 and 23 and the pressureresponsive faces 47a and 49a. Specifically, with the piston 15 to theright of its null position, communication is provided between the ports17 and 23 and the pressure responsive faces 49a and 47a, respectively.With the piston 15 to the left of its null position, it providescommunication between the ports 17 and 21 and the pressure responsivefaces 47a, and 49a, respectively. The pistons 15a and 15b resentsthe-position of the pistons with respect to null and the abscissarepresents time.

The lines designated 15, 15a and 15b represent the movement of thepistons 15, 15a and 15b, respectively. The slope of each of these linesrepresents the direction and rate of movement of the associated piston.Specifi-' cally, a positive slope represents the working stroke and anegative slope represents the return stroke. A zero slope representsdwell.

FIG. 4 also illustrates which of the pistons is providing a work outputduring each time interval with the designations 15, 15a and 15b alongthe abscissa. Generally, each of the pistons provides a work output forsubstantially the full working stroke thereof as shown in FIG. 4.

As each of FIGS. 1-3 represents the relative positions of the pistons atone point in time, each of these points can be located with reference toFIG. 4. Accordingly, the vertical lines designated FIG. 1, FIG. 2, andFIG. 3, respectively, in FIG. 4 correlate FIGS. 1-4.

' FIG. 5 shows a pressure transformer in the form of a pressure reducer11'. The pressure reducer 11 is identical to the pressure intensifier 11(FIGS. 1-3) in all respects not specifically shown or describedherein.Portions of the pressure reducer 11 corresponding to portions of thepressure intensifier 11 are designated by corresponding primed referencecharacters.

Functionally, the pressure reducer 11' differs from the pressureintensifier 1 l in that it reduces, rather than increase, the pressureof the fluid supplied to it. The pistons reduce the pressure of thefluid supplied thereto on the working stroke. Secondly, the pistons 15,15a

1 and 15b move on their working stroke as they move to sure intensifier11 are placed in communication with the return port 23 by passages 45,-45a, and 45b, respectively. With the pressure reducer 11', it is stillnecessary to provide a fluid flow path between the chamber sections 43',43a, and 43b and the return port. However, because the discharge andreturn ports have been reversed, it is necessary to eliminate thepassages 45, 45a and 45b and substitute therefor a passage which extendsfrom the chamber section 43' to the chamber section 43a to the chambersection 43b and from there to the groove 29b. The groove 29b is alwaysin communication with the return port 21 Thus, by this simple change,the chamber sections 43, 43a, and 43b are placed in communication withthe report port for all positions of the pistons 15', 15a and 15b.

In the position shown in FIG. 5, the piston 15' is at its null positionand is moving to the right on its return stroke. The piston 15a is at anextreme righthand position and is about to begin its working stroke, andthe piston b is at the extreme lefthand position and is the next pistonto move on a return stroke. v The chamber section 39 is in communicationvia the passage 61' with fluid at supply pressure from the inlet port17. The chambersection 41' is in communication via the passage 63' withthe return port 21'. Accordingly, the greater fluid pressure on the face47' forces the piston 15' to the right on its return stroke.

As the piston 15' moves to the right of its null position, the land 55uncovers the groove 33' to port fluid through the passage 63a to thechamber section 41a. Thus, fluid at relatively high supply pressure actson the pressure responsive face 49a". Simultaneously, the land53'vuncovers the groove 37 to thereby provide communication between thechamber section 39a and the discharge port 23!. Although the pressureresponsive face 47a is of greater effective area than the face 49a, thedischarge port 23 is coupled to a load having a pressure less than 'thepressure of the fluid supplied to the reducer 11 through the inlet 17'.Accordingly, by maintaining an appropriate relationship between therelative effective areas of the faces 47a and 49a and piston 15b to movethe right which in turn causes the piston 15' to move to the left. Thus,the pistons 15', 15a and 15b move in the same manner as describedhereinabove with reference to the pressure intensifier 11.

When the piston 15 is to the left of its null position, fluid at supplypressure is ported from the inlet port 17 to the chamber section 39a,and the chamber section 41a is open to the'return port 21'. Thus, thepiston 15a is moved to, or held in, the right-hand position.

Thus, the location of the piston 15' with respect to null controls thedirection of movement of the piston 15a.

The operation of the pressure reduceer 11, except to the extent notedabove, is identical to the operation of the pressure intensifier l1.

' Although exemplary embodiments of the invention have been shown anddescribed, many changes, modifications and substitutions may be made byone having ordinary skill in the art without necessarily departing fromthe spirit and scope of this invention.

1 claim:

1.. A pressure intensifier adapted for connection to fluid at a firstpressure level and to return wherein the pressure intensifier canincrease the pressure of the fluid from the first level to a secondlevel, said pressure intensifier comprising:

a plurality of pistons including first and second pistons;

body means for mounting said pistonsfor movement through working andreturn strokes;

means defining fluid passages extending between said first and secondpistons;

each of said pistons having surface means responsive to exposure tofluid under pressure for driving the piston on said working andreturnstrokes, each of said pistons increasing the fluid pressure tosaid second level on the working stroke thereof;

said. first piston porting fluid under pressure to the surface means ofthe second piston during at least a portion of one of the working andreturn strokes of said first piston to move said second piston on theother of its working and return strokes whereby the second piston ismoved on said other stroke during at least a portion of said one strokeof said first piston; and

valve means for controlling the fluid pressure applied to said surfacemeans of said first piston to move the first piston on the working andreturn strokes thereof.

2'. A pressure intensifier as defined in claim 1 wherein said one strokeis the working stroke and said other stroke is the return stroke.

3. A pressure intensifier as defined in claim 1 wherein said one strokeis the return stroke and said other stroke is the working stroke.

4. A pressure intensifier as defined in claim 1 wherein said surfacemeans of said second piston includes first and second faces of differenteffective areas, said fluid passages communicating with both of saidfaces, said first piston having a position in which it providescommunication between said first and second faces and fluid at the firstpressure level and return, respectively, to thereby move said secondpiston on said other stroke thereof.

5. A pressure intensifier connectible to fluid at supply pressure and toreturn for increasing the pressure of the fluid supplied thereto, saidpressure intensifier comprising:

a plurality of pistons including first, second, and .third pistons;

body means for providing first, second and third chambers in which saidfirst, second and third pistons can be reciprocated, each of said first,second and third pistons having a working stroke for increasing thepressure of the fluid supplied to the pressure intensifier and a returnstroke;

means for defining fluid passages between said first,

second and third chambers;

first valve means carried by said first piston and responsive to atleast a portion of the working stroke thereof to port fluid through saidpassage means to said second piston to move the second piston on itsreturn stroke; and

second valve means carried by said second piston and responsive to atleast a portion of the return stroke of said second piston for portingfluid through said fluid passage means to said third piston to move thethird piston on its working stroke.

6. A pressure intensifier as defined in claim 5 wherein said pressureintensifier has an outlet through which the fluid having increasedpressure can be discharged, said second valve means including means foropening said third piston to said outlet during at least the workingstroke of said third piston.

7. A pressure intensifier as defined in claim 5 wherein the second valvemeans is responsive to at least a portion of the returnstroke of thesecond piston to port fluid to said third piston to drive said secondpiston on its working stroke.

8. A pressure intensifier as defined in claim 6 wherein said secondpiston includes a first pressure responsive face, said pressureresponsive face and said body means defining a chamber section, saidfirst valve means porting fluid to said chamber section to act againstsaid first pressure responsive face to move said second piston on itsreturn stroke, said pressure responsive face acting 9 against said fluidin said chamber sectionon the working stroke of said second piston toincrease the pressure thereof.

9. A pressure intensifier as defined in claim including third valvemeans carried by said third piston responsive to at least a portion ofsaid working stroke of said third piston for porting fluid at supplypressure to said first piston to move the first piston on its returnstroke.

10. A pressure intensifier as defined in claim 5 wherein there are threeof said pistons.

11. A pressure intensifier as defined in claim 2 wherein the number ofsaid pistons is at least three and an odd number or a number which is aneven multiple of an odd number greater than one.

12. A pressure transformer for changing the pressure of fluid from afirst pressure level to a second pressure level comprising:

a plurality of pistons including first and second pistons;

body means for mounting said pistons for movement through working andreturn strokes, said body means having an inlet port for receiving fluidat the first pressure level, a discharge port through which fluid can bedischarged at a second pressure level, and an exhaust port through whichfluid can be exhausted from the body means; means defining fluidpassages extending from said ports to said first and second pistonswhereby each of said first and second pistons can be supplied with fluidat the first pressure level;- each of said pistons having surface meansresponsive to exposure to fluid at the first pressure level for drivingthe piston on said working and return strokes, each of said pistonschanging at least some of the fluid at the first pressure level suppliedto said second pressure level thereto on the working stroke thereof;first valve meanscarried by said first piston and responsive to thefirst piston being in a first position to port fluid at the firstpressure level through said passage means to said second piston and toopen a path through said passage means form the second piston to one ofexhaust and' discharge ports whereby the second piston is moved on oneof its strokes; and valve means for controlling the fluid pressureapplied ,to said surface means of said first piston to move the firstpiston on the working and return strokes thereof.

13. A pressure transformer as defined in claim 12 wherein said firstpressure level is higher than said second pressure level.

14. A pressure transformer as defined in claim 12 wherein said firstvalve means is responsive to said first piston being in a secondposition to port fluid at the first pressure level through said passagemeans to said second piston and to open a path through said passagemeans from said second piston to the other of said exhaust and dischargeports whereby the second piston is moved on the other of its strokes.

15. A pressure transformer comprising:

a plurality of pistons including first and second pistons, each of saidfirst and second pistons having at least first and second pressureresponsive faces;

body means for mounting saidpistons for reciprocating movement, each ofsaid pistons having a null position, said body means having first,second and third ports;

means-defining fluidpassages extending from said ports tosaid first andsecond pistons;

said first and second pressure responsive faces of said first and secondpistons being exposable to fluid to reciprocate the first and secondpistons; and

first valve means carried by said first piston and responsive to thefirst piston being on one side of its null position for providingcommunication through said passage means between said first and secondfaces of the second piston and the first and second ports, respectively,while blocking communication between the third port and said first andsecond facesof the second piston, said first valve means beingresponsive to the first piston being on the other side of its nullposition for providing communication through said passage means betweensaid first and second faces of the second piston and said second andthird ports, respectively, while blocking communication between saidfirst port and said first and second faces of the second piston.

16. A pressure transformer as defined in claim 15 wherein said pluralityof pistons includes a third piston, said third piston having at leastfirst and second pressure responsive faces, said second piston includingvalve means carried thereby for controlling the communication betweensaid ports and said first and second faces of said third piston, andsaid-third piston including valve means carried thereby for controllingthe communication between said ports and said first and second faces ofsaid first piston.

1. A pressure intensifier adapted for connection to fluid at a first pressure level and to return wherein the pressure intensifier can increase the pressure of the fluid from the first level to a second level, said pressure intensifier comprising: a plurality of pistons including first and second pistons; body means for mounting said pistons for movement through working and return strokes; means defining fluid passages extending between said first and second pistons; each of said pistons having surface means responsive to exposure to fluid under pressure for driving the piston on said working and return strokes, each of said pistons increasing the fluid pressure to said second level on the working stroke thereof; said first piston porting fluid under pressure to the surface means of the second piston during at least a portion of one of the working and return strokes of said first piston to move said second piston on the other of its working and return strokes whereby the second piston is moved on said other stroke during at least a portion of said one stroke of said first piston; and valve means for controlling the fluid pressure applied to said surface means of said first piston to move the first piston on the working and return strokes thereof.
 2. A pressure intensifier as defined in claim 1 wherein said one stroke is the working stroke and said other stroke is the return stroke.
 3. A pressure intensifier as defined in claim 1 wherein said one stroke is the return stroke and said other stroke is the working stroke.
 4. A pressure intensifier as defined in claim 1 wherein said surface means of said second piston includes first and second faces of different effective areas, said fluid passages communicating with both of said faces, said first piston having a position in which it provides communication between said first and second faces and fluid at the first pressure level and return, respectively, to thereby move said second piston on said other stroke thereof.
 5. A pressure intensifier connectible to fluid at supply pressure and to return for increasing the pressure of the fluid supplied thereto, said pressure intensifier comprising: a plurality of pistons including first, second, and third pistons; body means for providing first, second and third chambers in which said first, second and third pistons can be reciprocated, each of said first, second and third pistons having a working stroke for increasing the pressure of the fluid supplied to the pressure intensifier and a return stroke; means for defining fluid passages between said first, second and third chambers; first valve means carried by said first piston and responsive to at least a portion of the working stroke thereof to port fluid through said passage means to said second piston to move tHe second piston on its return stroke; and second valve means carried by said second piston and responsive to at least a portion of the return stroke of said second piston for porting fluid through said fluid passage means to said third piston to move the third piston on its working stroke.
 6. A pressure intensifier as defined in claim 5 wherein said pressure intensifier has an outlet through which the fluid having increased pressure can be discharged, said second valve means including means for opening said third piston to said outlet during at least the working stroke of said third piston.
 7. A pressure intensifier as defined in claim 5 wherein the second valve means is responsive to at least a portion of the return stroke of the second piston to port fluid to said third piston to drive said second piston on its working stroke.
 8. A pressure intensifier as defined in claim 6 wherein said second piston includes a first pressure responsive face, said pressure responsive face and said body means defining a chamber section, said first valve means porting fluid to said chamber section to act against said first pressure responsive face to move said second piston on its return stroke, said pressure responsive face acting against said fluid in said chamber section on the working stroke of said second piston to increase the pressure thereof.
 9. A pressure intensifier as defined in claim 5 including third valve means carried by said third piston responsive to at least a portion of said working stroke of said third piston for porting fluid at supply pressure to said first piston to move the first piston on its return stroke.
 10. A pressure intensifier as defined in claim 5 wherein there are three of said pistons.
 11. A pressure intensifier as defined in claim 2 wherein the number of said pistons is at least three and an odd number or a number which is an even multiple of an odd number greater than one.
 12. A pressure transformer for changing the pressure of fluid from a first pressure level to a second pressure level comprising: a plurality of pistons including first and second pistons; body means for mounting said pistons for movement through working and return strokes, said body means having an inlet port for receiving fluid at the first pressure level, a discharge port through which fluid can be discharged at a second pressure level, and an exhaust port through which fluid can be exhausted from the body means; means defining fluid passages extending from said ports to said first and second pistons whereby each of said first and second pistons can be supplied with fluid at the first pressure level; each of said pistons having surface means responsive to exposure to fluid at the first pressure level for driving the piston on said working and return strokes, each of said pistons changing at least some of the fluid at the first pressure level supplied to said second pressure level thereto on the working stroke thereof; first valve means carried by said first piston and responsive to the first piston being in a first position to port fluid at the first pressure level through said passage means to said second piston and to open a path through said passage means form the second piston to one of exhaust and discharge ports whereby the second piston is moved on one of its strokes; and valve means for controlling the fluid pressure applied to said surface means of said first piston to move the first piston on the working and return strokes thereof.
 13. A pressure transformer as defined in claim 12 wherein said first pressure level is higher than said second pressure level.
 14. A pressure transformer as defined in claim 12 wherein said first valve means is responsive to said first piston being in a second position to port fluid at the first pressure level through said passage means to said second piston and to open a path through said passage means from said second piston to the other of said exhaust and discharge ports wheReby the second piston is moved on the other of its strokes.
 15. A pressure transformer comprising: a plurality of pistons including first and second pistons, each of said first and second pistons having at least first and second pressure responsive faces; body means for mounting said pistons for reciprocating movement, each of said pistons having a null position, said body means having first, second and third ports; means defining fluid passages extending from said ports to said first and second pistons; said first and second pressure responsive faces of said first and second pistons being exposable to fluid to reciprocate the first and second pistons; and first valve means carried by said first piston and responsive to the first piston being on one side of its null position for providing communication through said passage means between said first and second faces of the second piston and the first and second ports, respectively, while blocking communication between the third port and said first and second faces of the second piston, said first valve means being responsive to the first piston being on the other side of its null position for providing communication through said passage means between said first and second faces of the second piston and said second and third ports, respectively, while blocking communication between said first port and said first and second faces of the second piston.
 16. A pressure transformer as defined in claim 15 wherein said plurality of pistons includes a third piston, said third piston having at least first and second pressure responsive faces, said second piston including valve means carried thereby for controlling the communication between said ports and said first and second faces of said third piston, and said third piston including valve means carried thereby for controlling the communication between said ports and said first and second faces of said first piston. 